Construction of magnetic compasses



1944- J. M. s. KAUFMAN ETAL 2,361,548

CONSTRUCTION OF MAGNETIC COMPASSES Filed July 11, 1941 2 Sheets-Sheet l gvwcmms JmgvkZKEAZW Oct 1944, J.' M. s. KAUFMAN ET AL 2,361,548

CONSTRUCTION QF MAGNETIC COMPASSES Filed July 11, 1941 2 Sheets-Sheet 2 perfect the soldered joints.

Patented Oct. 31, 1944 um'rso STATES CONSTRUCTION or MAoNErrIo-cmvrmss-Es Joseph M. S Kaufman, Washington,D. (3., Shel ley Krasnow, New York County, N. 'Y., and Josef A. Schaerfl, Arlington County, Va.

Application July 11, 1941, Serial No. 402,030

6 Claims. (Cl. 33-223) This invention relates to magnetic compasses of the type ordinarily used on ships. The invention is particularly drawn to such magnetic instruments as are used in the presence of corrosive fluid, which fluid may be either air having corrosive constituents, or liquid contained within the bowl forming the outer casing of the said compass. I

It is an object of the invention to provide corrosion resisting surfaces which may be easily and economically applied, which surfaces will afterwards permit repair with facility, will avoid any magnetic difliculties and will provide a pleasant dull .surface of non-glaring quality, resembling white paint.

It :is a further object of the invention to providea superiorcorrosion resisting base for paint to be applied under corrosive conditions. It is a further object of the invention to provide a corrosion resistant and adherent coating for permanent magnet material having high proportions of aluminum. It is a further object -;of the invention to provide a means for coating the moving system of compasses, which parts are joined with :solder, the said coating serving to t.is a further object oftheinventiontoprovide a mannerofcoating the said portions'of the compass in such a manner as to avoid development of undesired strain during the coating operation. It is .a further object of the invention to perfect the corrosion-resistant properties of such compasses and to correct .any injuries done by abrasion or otherwise.

While-a specific type of 1iquid-filled compass isdescribed herein, it will be understood that the same type of construction may be applied under other conditions where corrosion exists. Such mode of fabrication mayralsobe employed wherever it is desired to .apply paint to .lnetallic surfaces to obtain good bonding.

Such techniques may also be vapplied to any other objects which are fabricated of separate soldered parts, 'which are required to .be either leakproof or corrosion-proof, 'or to have an attractive non-glare surface. urther still, the technique described herein .may be applied to magnet materials of any nature or of any shape although it is particularly applicable to those having a, significant aluminum content. Such materials may be utilized either inside .or' outside of magnetic indicating instruments and may be employed in electromagnetic or magnetic devices. of any "type where corrosive. conditions are found.

Other objects and advantages of the invention will be evident from the following :d-rawings in which: v

Figure :1 indicates a general ,cross-seetional. viewof an instrument constructed according to theinvention. 1

Figure 2 shows a top 'view of an instrument such as shown in Figure 1. 1

Figure 3 shows the bottom view -of the ,moving-system-of-this instrument.

Figure 4 shows .aportion of the -.dial of the instrument as shown dnEigure 3.

Figure --5 shows ,a cross-sectional view of ;a portion of the dial shown'in Figure .4, 1taken across the line .5 --.5.

Figure 6 shows a longitudinal cross-sectional view of a cylindrical zbar1-1=nagnet plated iaccording .to the method of theinvention.

Referring :now to Figure ,1, '-l ,rShOsVVS the outer casing or'bowl of .acon pass which is ordinarily used for :steeri-ngqships 'andboats. This bowl-is covered with a transparent cover :2. At the, sides :of :the bowl -.-,i are knifeedges 3, upon which the entire zcompassrests. At the lower part of thebowl it is anv-expansio-n .chamberusually made of corrugated metal and represented ask. The compasslis closed at the bottom by acover which may or maynot lee-transparent and is (designated .as ,5. Within the ,bowl is a pivotsupport-fi upon which :rests. .a pivot l Upon this pivot, mounted .so as .to :be free torotate about any ,axis, is the :moving system '8. This moving system is {ordinarily observable through the :topof the glass cover 2, and;.-has:mounted upon it magnets 19, *9, and Ill, ,lq, which :orient itpi 'the direction of the magnetic meridian.

The moving system 1-8 is morefully shown in Figure 3. .Here'gaadiahisrepresented-as 1-0. This dial isin the ;f orm of 1a ,rimbf metal, which is formed :with=-overhanging portions so 3 5,110 stiifen it. ltiisiastened byrmeans of channel shaped members or tubes l5,;t.o.-a floatas sembly indicated as 1 In Figures 1 and 3, thezouterdial, the connecting tubes or channels |a5,- a-nd .the -float member H :composed of an upper ,part and ;a ,lower part are shown. lEastened @to; the ebottomcf -,the float l l in adjustable; fashion are, magnets .9, :9, and I0, 10. These areheldbyplamps il.3,;l3, so-asto be movable pover ,a limited range and ,to:a11ow orienting themagnetsifl, :9, and v I 0, FIB, ,to obtain the correct settin of the-card relative .to-the magneticimeridian. V

With these clamps-the magnetsgmay'be'moved forward or backward to balance athecard in the direction of their length. They may also be shifted bodily sidewise, or may be twisted slight- 1y. Thus, by moving the clamps and shifting the magnets, one-can balance the card and magnet assembly and can also orient the magnetic axis so that it coincides with the geometric North- South axis of the moving system.

A portion of the card or dial lfiis shown in Figure'5. Here the lines and numerals are shown as being out completely through the metal so as to be permanent and ineffaceable. If the card is illuminated from below, these figures and lines appear especially distinct. Alternatively, the lines and numerals cut through the metal may be filled either with a paint or with a luminous material, thus providinga firm bond and an accurate location for the paint. I

In use the bowl shown in Figure I is ordinarily filled with liquid M. This is often a mixture of alcohol and water, which has intrinsic unavoidable corrosive properties. Metals without Protecting coating will sufier extreme corrosion if placed in this liquid. Where the liquid is omitted from the bowl, the air itself, especially in marine atmospheres, may have considerable corroding power. All parts of and especially the interior of the bowl I must therefore be protected against corrosion.

Furthermore, since readings are to be made and since the illumination available is often weak, the interior of the bowl should be of a light color.

Further still, because sun occasionally shines upon the compass, it is necessary that the interior be of a non-glaring nature. In the normal use of the compass, it is often mounted in a binnacle which serves to support it and also to provide illumination. This illumination is often furnished by a light above or below the compass. In either case, the light will introduce glare if any brightly reflecting surfaces are present inthe compass.

In the present invention the following procedure is followed in order to fabricate the bowl I. Such a bowl is often made of bronze, brass, copper, or some other non-magnetic material.

- To the bottom of this bowl is then soldered the expansion chamber or capsule 4,1 the joint being made with ordinary soft solder made of tin and lead. The interior of the bowl is next covered electrolytically with a deposit of tin [1, applied in a manner which will be hereinafter described. The coating of tin is applied simultaneously to the interior of the expansion chamber, theinterior of the bowl, and to all of the soldered joints.

-Tin is' particularly beneficial for this purpose,

since in the proper sort of bath it has great throwing power. Thus, it will seek out and cover minute crevices, porous spots, small holes, etc. If any such porous or open spots exist in the casing l', providing they are not too large; they will be sealed efiectively by the tin coating. The same 1 applies ,to'any' defects which may" existin the soldered joints between the expansion capsule 4,

and the bowl I, -or indeed between the parts of theexpansion capsule'itself. 4

It is "to be emphasized here that the beneficial effects of using tin for the various parts of the compass arise from its application by electrolytic deposition from the proper sort of solution. In the case of the magnets, since these are often provided in rough cast form, they will'have a number of deep pits and blow-holes. 'Thej tin will throw or depositin these cavities, preventing the opportunities for later corrosion, which would be observed with other types'of plating. V

Inthe case of the interior of the bowl, here also,

one usually uses a cast bowl and although this is often machined on the interior, there will be the inevitable porous spots and blow-holes in the interior surface. Here also, tin deposited properly will protect the metal in these cavities and prevent later corrosion therein. Further still, the interior of the bowl is of complicated shape and has re-entrant surfaces, particularly in the interior of the expansion chamber. Because of the extreme throwing power in the technique described, the tin will be deposited in ample quantity on all the surfaces in one simple operation.

In thecase of the card assembly, referred to below, it will be seen that there also, there are a number of re-entrant surfaces and cavities which will be properly plated due to the throwing power of the tin. Furthermore, the plating of the assembled moving system hereinafter described, is possible because of the throwing power of the tin in the bath described. Were other materials or other techniques to be utilized, the plating of the assembled piece would be futile, since it would be impossible to obtain deposition of metal in the many crevices present in an assembled piece, and it is precisely in these crevices that the coating previously applied is most apt to be abraded and to require protection.

The coating of tin applied in the manner taught herein is crystalline in nature. When viewed with the naked eye, such a surface ap-' pears a dull grayish white, giving a pleasing appearance resembling dull white paint.

further coating. However, where paint is desired,

it can be applied to the interior of the bowl I after the crystalline deposit of tin has been placed. This crystalline deposit, being formed of minute particles or minute crystals of tin, provides a roughened surface to which paint adheres better than to the smooth surface left by hot tinning.

A suitable coating for the interior of the compass bowl is a paint made with vinyl resin. This can be made white with some pigment such as titanium oxide, and after application and drying will be found to resist the solvent action of alco hol and water. It will also resist the solvent action of other organic liquids which may be used as the compass fluid. Alternatively, the vinyl resin may be formed in the shape of a liner and pressed into the interior of the bowl. A white paint made with vinyl resin may also be applied to the moving system. This paint may bemade very thin in contradistinction to the albumin paint previously used. The latter had to be used in thickened form. The paint made with vinyl resin may be so thin that it will not fill any graduations which are cut through the moving system. The vinyl resin paint need not have any great covering power, since the unclercoat of crystalline tin has a whitish color.

In the case .of the moving system, such as shown in Figure 3, the dull or crystalline tin provides a particularly effective coating for such a member as shown n detail in Figure5. Because of the throwing. ower of the tin, the vertical wall left by cutting away the metal will be effectively coated and will resist corrosion. Furthermore, the surface of the dial will have a particularly pleasing dull appearance, such as described before for the interior of the bowl. The float portion I l, coated in the same way, will have the same corrosion resistance as described before and will presentthe same pleasing grayish-white ap pearance.

Such a. surface is entirely suitable for use, without any The coating has particular advane used electrolyticallyin a highly alkalinebathgin the manner described herein-,fwill c'oat 'Alnico properly, so :as to make it completely": resistant to corrosion. The tin 'appearsftoa'dher'e well andto'fill the crevices and pores which are oftempresent iin cast Alnicomaterial. Tests on immersion ofisu'ch magnets in solutions having different corrosive properties, such astsalt water, pure alcohl,:and mixtures of alcoholandwater, all 'sho'w that'ithe tin provides an adequate and satisfactory corrosionresistantcoating.

.Arsatisfactory plating bath'fortheAlnico magnet material can be prepared as follows: i

To one gallon of water is .addedllfi :ouncesof sodiumstannate, one ounce of sodiumhydroxide, two ounces of sodium acetate, approximately of :an ounce of fresh hydrogen peroxide, and about of an ounceof 'borax. Heatisapplied-to bringthe bath to a temperature of about.150 A voltage of about 6 volts is applied, andca curren't density of about 3.0 amperes perssquarefoot of surface area being plated. The anode :should not be of too, large'areaand should be s'Of-JSllCh area that the current density at the anode is about 3.0 amperes per square foot. :Itisneces sary that the currentzdensity figure herewith be utilized, since part of .the success :of the: plating operation depends upon this. i

Before plating the Alnico'magnet materiaLit should be ground onsomesort of abrasive-wheel to remove most of the scale and surfacedirt. It is-then cleaned with pumice,.preferably' in alzpaste made with Water. Contrary to the. practice usu-. ally followed in plating, it has been found best'xto avoida chemical cleaning treatment for thisymaterial. a The plating technique, namely the cleaning with pumice and water, and the composition and other details concerning the plating bath may also be followed for the plating of brass, bronze, :or copper parts to housed in the constructionof a compass. For the other parts of thezcompass-described herein, it is understood that the mode of plating will be substantially the same as that described for the plating technique of the Alnico magnet material. I

The plating technique described herein may be modified and other means used to obtain the same result. The specific method and composition of the bath disclosed is intended to serve as an example by which successful results may be obtained.

Figure 6 shows a longitudinal cross-sectional view of a cylindrical Alnico magnet 9 covered with an electroplated coating of tin l8.

A precaution desirable in the plating of magnets is that they be plated in the unmagnetized condition. Magnetized material will pick up small pieces of iron and steel, which will project through the plating and subsequently corrode, leaving rust spots. If the magnets must be plated the magnetized condition, an adhering arson or steelshown he removed carefully, and a set of magnets had best b'e -pla'ced in the bath permanent'ly to pichup any particles of-magnetic :or terrous -materi'a1 which might fall into the :bath.

lif the magnets have a very rough :surface, it is considered advisableto plate them with tin, work down the: coating with .a rotary scratch brush. or wire :brush, and'to'applyia coating. ofitin "outside the :brushe'dcoating. 1 This process may be .repeated. several times, .The brush utilized should preferably -hav'ewbrass wires. The usual type of steelTwire brush is too apt to leave :small :steel particles upon the magnet. .These will later cause :difficulty :whenfithe -magnets IaI'GUIJIatG'G The. finalacoating of tinis-best made over /1000 of an inchin thickness,..and may be .made .much thicker. An additional: advantage of coating the magnetwith tin is that soft solderingrmay be done directly to :the coating. The usual Alnico'magnet material will :not allow such soft. soldering.

.Althoughthe plating-process and products have been disclosed for :Al-n-ico magnet material, it is obviousthat this technique may be applied to any other permanent magnet material where the same problemsappear. It may be app-liedto any other magnet compositionwhich has a large proportion of aluminum,- which aluminum tends to prevent electroplating by usual methods. Al-

ternatively, it maybe applied-to anyof the 'other ferrousalloys having; aluminum a an ingredient. The, possibility of soft soldering mentioned abovehas particular application to magnetic in-' strument construction. Thus tin-plated magnets 1' maybe soldered to a-holder, which is clamped to oryotherwise fastened in adjustable relation to a moving system of a compass.

If .thecomposition andcurrent density taught herein are utilized, and if the proper temperature astaught herein is utilized, it will be found that the tin will be deposited in crystalline-condition. The-moving system will thushave .a dull grayish-white appearance, free from glare. This presen'tsa pleasing. surface, and one which does not fatigue the eyes in long observation.

The fioat and' card assembly may be :madeof sheet'brass', with "the various portions spun or die'formed. The coating of tin as disclosed herein, willact as complete protection against corrosion. It Will provide a good bond for solder, should repair of .the instrument be necessary. It will also facilitate the renewal ofjtlie' coating. All. that need be done is to give the card'and float assembly'a chemical cleaning treatment, followed by replating' in the same type of bath. 7 After this type of plating, the system will have theappearance of an entirely new 'unit, and will not Show the marred surfaces suggestive of a repaired unit.

.itft'er thecard assembly has been plated and afterthe "various small parts, such as screws, magnets, and other removable elements entering into the assembly of the card have been placed in their proper position, and the card completely assembled, it may be put into the plating bath for a short time to receive a final coat of tin. Thus, any spot which has been left open by error or from which the tin has been abraded in handling will be coated and thus protected from corrosion.

When the card assembly has been completely assembled, with the magnets, clips, screws, and other parts, the entire assembly may be placed in the plating bath for a final thin coat of tin.

The exceptionally high throwing power of tin will allow it to reach deep into the crevices.

Likewise any very small hole in the bowl or expansion chamberwillrbe filled with tin. The coating will also allow easy soldering, should .repair b required, since tin forms a very good foundation for soft solder. Thesame dull finish above referred to will .be deposited on the inside of the bowl. This will provide a satisfactory grayish-white surface, which will make for easy reading and the reflection of light withinthe bowl, without a the development of any metallic glare. The surface can be renewed easily, should it be injured, in the same manner as indicated in the discussion of the plating of the card assembly above. However, should it be desired to paint the interior with white paint, the crystaL line, or roughened surface will provide a far bet ter foundation for the paint than the smooth surface usually left'by hot tinning. In the past, an albumin paint, usually made of egg white and white lead has been used. This has been found to adhere very well to the tinfoundation. A better coating is a paint made up of some white pigment such as titanium white in a vehicle such as vinyl resin. Such a coating is impervious to alcohol, is easier to apply than the albumin paint indicated above, and will adhere exceptionally well to the tin undercoating. However, if the paint is omitted, a perfectly'satisfactory surface will result.

I It has been found that the plated coating of tin for the interior of the bowl and for the moving system have great advantages in the operation of'the compass. Since in the movement of the moving system within the bowl, the liquid is set in motion, the'material having least adhesion to the liquid will be best as a coating. The parts will then adhereless strongly to and be less retarded by the liquid. Although the plated coating has a type of roughness, it is of a microscopic degree, as compared with that which will be noted in paint. The moving system will there,- fore move with less hindrance through the liquid and the, response of the compass will be superior to that of a system inwhich other materials are employed. Similarly, the liquid moving inside the bowl will move with least hindrance if the bowl is made relatively smooth. The plated coating-is smoother than the paint customarily used and there will therefore be less of the type of error known as swirl. I

Although the above method has been shown as appliedto a compass which'employs liquid contained therein, it may obviously be applied to a similar instrument which operates without 7 to plate non-metallic piecesby the same techf with liquid when in use, the said bowl having an interior surface exposed to liquid and exposed to View when in normal use, the said bowl being covered with a crystalline deposit of tin, the said tin serving the function of sealing porous portions of the bowl, protecting the said bowl against corrosion and providing a dull surf-ace resembling white paint.

2. A bowl as in claim 1, with the addition of a metallic expansion chamber, the said chamber being fastened together with solder and being v coated after soldering with a plated deposit of tiny i 3. In a magnetic compass, a moving system adapted to point in the direction of the magnetic meridian, the said moving system being made of metal and forming a float portion adapted to be immersed in liquid, the said float portion being coated with a crystalline deposit of tin, thereby protecting the said member against corrosion, sealing any porous or open portions, and furnishing a non-glaring surface resembling white paint.

4.- In a magnetic instrument, an indicating dial, the said dial having graduations and characters out completely therethrough, the said dial being immersed in liquid when in normal use, a

coating of crystalline tin on the said dial, the said coating serving to protect the'cut and uncut portions against corrosion, further serving to provide a dull surface of non-glaring properties, resembling white paint.

5. As an article Of manufacture, a permanent magnetcomposed of material having an appreciable aluminum content, the said magnet being covered with an electrodeposited coating of tin.

6. A painted metal surface adapted to be exposed to corrosive fluids, the said painted surface being applied upon an undercoating of metal which is subject to corrosion, the said metal having upon it a crystalline deposit of tin, the paint being applied over the said crystalline deposit of tin, the said deposit providing a corrosion resisting coating for the metal and further providing a firm foundation for the paint.

JOSEPH M. s. KAUFMAN. SHELLEY KRASNOW. JOSEF A. SCI-IAERFL. 

